β-cell dysfunction rather than insulin resistance is the main contributing factor for the development of postrenal transplantation diabetes mellitus

Background. Our study was undertaken to investigate the pathogenesis and possible risk factors for postrenal transplantation diabetes mellitus (PTDM). Methods. We recruited 114 patients with normal glucose tolerance (NGT) and performed both 75-g oral glucose tolerance tests (OG;TT) and short insulin tolerance tests 1 week before and 9-12 months after transplantation. Results. The subjects were classified into three groups by World Health Organization criteria on the basis of OGTT after transplantation: (a) 36 (31.6%) subjects with normal glucose tolerance; (b) 51 (45.7%) subjects with impaired glucose tolerance (IGT); and (c) 27 (23.7%) subjects with postrenal transplantation diabetes mellitus. Dosages of steroid and cyclosporine were equivalent among the three groups. Before transplantation, the fasting and 2-hr plasma glucose and proinsulin/insulin (PI/I) ratios were significantly higher in the IGT and PTDM groups than in the NGT group, but the insulin sensitivity index (ISI) was not significantly different among the three groups. In addition, the area under the curve-insulin on OGTT was significantly lower in the PTDM group than in the NC;T group. After transplantation, however, the ISI was increased in all groups. Furthermore, the ISI and PI/I ratios revealed significantly higher values in the PTDM group than in the NGT group after transplantation. Conclusions. These results revealed that fasting and 2-hr plasma glucose levels, as well as the proinsulin/ insulin ratio before transplantation, are both possible indicators of beta -cell dysfunction and may be predictors for the development of PTDM. Furthermore, beta -cell dysfunction, rather than insulin resistance, was proven to be the main factor for the pathogenesis of PTDM.